For finish coating of interior and exterior building materials such as concrete structures, prestressed concrete (PC) panels, aerated concrete (ALC) panels, and slate panels, hitherto cement, acrylic, epoxy and cellulosic finish coating compositions have been used as well as synthetic resin emulsion paints.
These finish coating compositions, however, are too hard to follow cracks which can occur in the underlying substrate. If cracks occur in the substrate, then cracks will also appear in the finish coating, resulting in the coating being lifted and separated near the cracks and thereby base its water-proof function.
To improve the crack-following and water-proof capabilities that the hard finish coating compositions lack, there are known elastic finish coating compositions which have both the water-proofness and decorative effect, for example, acrylic rubber, acrylic resin, chloroprene rubber and urethane rubber base finish coating compositions. These elastic finish coating compositions are used in single and multi-layer forms, for example, by applying solutions of acrylic urethane resins and acrylate resins as protective and decorative coatings.
Coatings of these organic elastic finish coating compositions show elastomeric behavior enough to follow cracks which can occur in the underlying substrate, restricting the appearance of cracks on the exterior surface thereof. The organic elastic finish coating compositions, however, are not only poor in flame retardance and low-temperature elongation, but also have low moisture permeability so that moisture can condense at the interface between the coating and substrate, causing blisters and freezing damages to the coatings.
Finish coating compositions based on silicone rubber were proposed to eliminate these drawbacks. The silicone base elastic finish coating compositions are generally classified into the solution and emulsion types depending on whether room-temperature vulcanizable silicone rubber is dissolved in a solvent or dispersed in water. The silicone elastic finish coating compositions of either type show elastomeric behavior and can follow cracks which can occur in the underlying substrate like the above-mentioned organic elastic finish coatings compositions, and at the same time, exhibit improved temperature-sensitive performance from low temperatures of the order of -20.degree. C. to high temperatures of the order of 60.degree. C. as well as improved moisture permeability and flame retardance due to the silicone polymer structure.
Despite these performance advantages, the silicone base elastic finish coating compositions lack decorative effect. More particularly, silicone elastic coatings are susceptible to stain and from a maintenance aspect, difficult to cover with another resin.
Techniques of blending EPDM or the like are known to overcome these drawbacks of the silicone base elastic finish coating compositions, but the resulting coatings exhibit excessive rubbery nature beyond the acceptable level. Moreover, Japanese Patent Application Kokai No. 267377/1987 discloses a flame retardant elastomeric finish coating composition for interior and exterior uses comprising in admixture, a thermoplastic resin emulsion and a silicone base aqueous emulsion, with various additives added and dispersed therein. This is not satisfactory in stain proofness, flame retardancy, and shelf stability.